Improvements to Razor Components. There's a single project template now, Razor components support endpoint routing and prerendering, and Razor components can be hosted in Razor class libraries. There's also improved event handling and support for forms and validation.

Runtime compilation. It was disabled in ASP.NET Core 3.0 templates but it can be turned on now by adding a special NuGet package to the project.

Worker Service template. Need to write a Windows service or Linux daemon? Now we have a worker service template for this.

gRPC template. Together with Google, Microsoft is building a gRPC that is popular with the Remote Procedure Call (RPC) framework. This release of ASP.NET Core introduces the first bits of gRPC support on ASP.NET Core.

The Angular template is using Angular 7. The Angular SPA template uses now Angular 7 and before the first stable release it will be replaced with Angular 8.

Authentication for SPAs. Microsoft added out-of-the-box authentication support for single-page applications with this preview.

SignalR integration with endpoint routing. Small change - SingalR routes are now defined with endpoint routing.

SignalR Java client support for long polling. The SignalR Java client can be used now even in environments where WebSocket is not supported or allowed.

There's not much news about Entity Framework Core 3.0 but we can expect updates with next preview version of .NET Core.